﻿// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.


#if NETFX || NETSTANDARD2

//注：此文件代码来源 .net 6 以上版本

using System.Diagnostics;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;


// Some routines inspired by the Stanford Bit Twiddling Hacks by Sean Eron Anderson:
// http://graphics.stanford.edu/~seander/bithacks.html

namespace Chloe.Numerics
{
    /// <summary>
    /// Utility methods for intrinsic bit-twiddling operations.
    /// The methods use hardware intrinsics when available on the underlying platform,
    /// otherwise they use optimized software fallbacks.
    /// </summary>
    public static class BitOperations
    {
        //        // C# no-alloc optimization that directly wraps the data section of the dll (similar to string constants)
        //        // https://github.com/dotnet/roslyn/pull/24621

        //        private static ReadOnlySpan<byte> TrailingZeroCountDeBruijn => new byte[32]
        //        {
        //            00, 01, 28, 02, 29, 14, 24, 03,
        //            30, 22, 20, 15, 25, 17, 04, 08,
        //            31, 27, 13, 23, 21, 19, 16, 07,
        //            26, 12, 18, 06, 11, 05, 10, 09
        //        };

        //        private static ReadOnlySpan<byte> Log2DeBruijn => new byte[32]
        //        {
        //            00, 09, 01, 10, 13, 21, 02, 29,
        //            11, 14, 16, 18, 22, 25, 03, 30,
        //            08, 12, 20, 28, 15, 17, 24, 07,
        //            19, 27, 23, 06, 26, 05, 04, 31
        //        };

        //        /// <summary>
        //        /// Evaluate whether a given integral value is a power of 2.
        //        /// </summary>
        //        /// <param name="value">The value.</param>
        //        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        //        public static bool IsPow2(int value) => (value & (value - 1)) == 0 && value > 0;

        //        /// <summary>
        //        /// Evaluate whether a given integral value is a power of 2.
        //        /// </summary>
        //        /// <param name="value">The value.</param>
        //        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        //        [CLSCompliant(false)]
        //        public static bool IsPow2(uint value) => (value & (value - 1)) == 0 && value != 0;

        //        /// <summary>
        //        /// Evaluate whether a given integral value is a power of 2.
        //        /// </summary>
        //        /// <param name="value">The value.</param>
        //        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        //        public static bool IsPow2(long value) => (value & (value - 1)) == 0 && value > 0;

        //        /// <summary>
        //        /// Evaluate whether a given integral value is a power of 2.
        //        /// </summary>
        //        /// <param name="value">The value.</param>
        //        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        //        [CLSCompliant(false)]
        //        public static bool IsPow2(ulong value) => (value & (value - 1)) == 0 && value != 0;

        //        /// <summary>
        //        /// Evaluate whether a given integral value is a power of 2.
        //        /// </summary>
        //        /// <param name="value">The value.</param>
        //        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        //        internal static bool IsPow2(nint value) => (value & (value - 1)) == 0 && value > 0;

        //        /// <summary>
        //        /// Evaluate whether a given integral value is a power of 2.
        //        /// </summary>
        //        /// <param name="value">The value.</param>
        //        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        //        internal static bool IsPow2(nuint value) => (value & (value - 1)) == 0 && value != 0;

        //        /// <summary>Round the given integral value up to a power of 2.</summary>
        //        /// <param name="value">The value.</param>
        //        /// <returns>
        //        /// The smallest power of 2 which is greater than or equal to <paramref name="value"/>.
        //        /// If <paramref name="value"/> is 0 or the result overflows, returns 0.
        //        /// </returns>
        //        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        //        [CLSCompliant(false)]
        //        public static uint RoundUpToPowerOf2(uint value)
        //        {
        //            if (Lzcnt.IsSupported || ArmBase.IsSupported || X86Base.IsSupported)
        //            {
        //#if TARGET_64BIT
        //                return (uint)(0x1_0000_0000ul >> LeadingZeroCount(value - 1));
        //#else
        //                int shift = 32 - LeadingZeroCount(value - 1);
        //                return (1u ^ (uint)(shift >> 5)) << shift;
        //#endif
        //            }

        //            // Based on https://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
        //            --value;
        //            value |= value >> 1;
        //            value |= value >> 2;
        //            value |= value >> 4;
        //            value |= value >> 8;
        //            value |= value >> 16;
        //            return value + 1;
        //        }


        //        /// <summary>
        //        /// Round the given integral value up to a power of 2.
        //        /// </summary>
        //        /// <param name="value">The value.</param>
        //        /// <returns>
        //        /// The smallest power of 2 which is greater than or equal to <paramref name="value"/>.
        //        /// If <paramref name="value"/> is 0 or the result overflows, returns 0.
        //        /// </returns>
        //        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        //        [CLSCompliant(false)]
        //        public static ulong RoundUpToPowerOf2(ulong value)
        //        {
        //            if (Lzcnt.X64.IsSupported || ArmBase.Arm64.IsSupported)
        //            {
        //                int shift = 64 - LeadingZeroCount(value - 1);
        //                return (1ul ^ (ulong)(shift >> 6)) << shift;
        //            }

        //            // Based on https://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
        //            --value;
        //            value |= value >> 1;
        //            value |= value >> 2;
        //            value |= value >> 4;
        //            value |= value >> 8;
        //            value |= value >> 16;
        //            value |= value >> 32;
        //            return value + 1;
        //        }

        //        /// <summary>
        //        /// Count the number of leading zero bits in a mask.
        //        /// Similar in behavior to the x86 instruction LZCNT.
        //        /// </summary>
        //        /// <param name="value">The value.</param>
        //        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        //        [CLSCompliant(false)]
        //        public static int LeadingZeroCount(uint value)
        //        {
        //            if (Lzcnt.IsSupported)
        //            {
        //                // LZCNT contract is 0->32
        //                return (int)Lzcnt.LeadingZeroCount(value);
        //            }

        //            if (ArmBase.IsSupported)
        //            {
        //                return ArmBase.LeadingZeroCount(value);
        //            }

        //            // Unguarded fallback contract is 0->31, BSR contract is 0->undefined
        //            if (value == 0)
        //            {
        //                return 32;
        //            }

        //            if (X86Base.IsSupported)
        //            {
        //                // LZCNT returns index starting from MSB, whereas BSR gives the index from LSB.
        //                // 31 ^ BSR here is equivalent to 31 - BSR since the BSR result is always between 0 and 31.
        //                // This saves an instruction, as subtraction from constant requires either MOV/SUB or NEG/ADD.
        //                return 31 ^ (int)X86Base.BitScanReverse(value);
        //            }

        //            return 31 ^ Log2SoftwareFallback(value);
        //        }

        //        /// <summary>
        //        /// Count the number of leading zero bits in a mask.
        //        /// Similar in behavior to the x86 instruction LZCNT.
        //        /// </summary>
        //        /// <param name="value">The value.</param>
        //        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        //        [CLSCompliant(false)]
        //        public static int LeadingZeroCount(ulong value)
        //        {
        //            if (Lzcnt.X64.IsSupported)
        //            {
        //                // LZCNT contract is 0->64
        //                return (int)Lzcnt.X64.LeadingZeroCount(value);
        //            }

        //            if (ArmBase.Arm64.IsSupported)
        //            {
        //                return ArmBase.Arm64.LeadingZeroCount(value);
        //            }

        //            if (X86Base.X64.IsSupported)
        //            {
        //                // BSR contract is 0->undefined
        //                return value == 0 ? 64 : 63 ^ (int)X86Base.X64.BitScanReverse(value);
        //            }

        //            uint hi = (uint)(value >> 32);

        //            if (hi == 0)
        //            {
        //                return 32 + LeadingZeroCount((uint)value);
        //            }

        //            return LeadingZeroCount(hi);
        //        }

        //        /// <summary>
        //        /// Returns the integer (floor) log of the specified value, base 2.
        //        /// Note that by convention, input value 0 returns 0 since log(0) is undefined.
        //        /// </summary>
        //        /// <param name="value">The value.</param>
        //        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        //        [CLSCompliant(false)]
        //        public static int Log2(uint value)
        //        {
        //            // The 0->0 contract is fulfilled by setting the LSB to 1.
        //            // Log(1) is 0, and setting the LSB for values > 1 does not change the log2 result.
        //            value |= 1;

        //            // value    lzcnt   actual  expected
        //            // ..0001   31      31-31    0
        //            // ..0010   30      31-30    1
        //            // 0010..    2      31-2    29
        //            // 0100..    1      31-1    30
        //            // 1000..    0      31-0    31
        //            if (Lzcnt.IsSupported)
        //            {
        //                return 31 ^ (int)Lzcnt.LeadingZeroCount(value);
        //            }

        //            if (ArmBase.IsSupported)
        //            {
        //                return 31 ^ ArmBase.LeadingZeroCount(value);
        //            }

        //            // BSR returns the log2 result directly. However BSR is slower than LZCNT
        //            // on AMD processors, so we leave it as a fallback only.
        //            if (X86Base.IsSupported)
        //            {
        //                return (int)X86Base.BitScanReverse(value);
        //            }

        //            // Fallback contract is 0->0
        //            return Log2SoftwareFallback(value);
        //        }

        //        /// <summary>
        //        /// Returns the integer (floor) log of the specified value, base 2.
        //        /// Note that by convention, input value 0 returns 0 since log(0) is undefined.
        //        /// </summary>
        //        /// <param name="value">The value.</param>
        //        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        //        [CLSCompliant(false)]
        //        public static int Log2(ulong value)
        //        {
        //            value |= 1;

        //            if (Lzcnt.X64.IsSupported)
        //            {
        //                return 63 ^ (int)Lzcnt.X64.LeadingZeroCount(value);
        //            }

        //            if (ArmBase.Arm64.IsSupported)
        //            {
        //                return 63 ^ ArmBase.Arm64.LeadingZeroCount(value);
        //            }

        //            if (X86Base.X64.IsSupported)
        //            {
        //                return (int)X86Base.X64.BitScanReverse(value);
        //            }

        //            uint hi = (uint)(value >> 32);

        //            if (hi == 0)
        //            {
        //                return Log2((uint)value);
        //            }

        //            return 32 + Log2(hi);
        //        }

        //        /// <summary>
        //        /// Returns the integer (floor) log of the specified value, base 2.
        //        /// Note that by convention, input value 0 returns 0 since Log(0) is undefined.
        //        /// Does not directly use any hardware intrinsics, nor does it incur branching.
        //        /// </summary>
        //        /// <param name="value">The value.</param>
        //        private static int Log2SoftwareFallback(uint value)
        //        {
        //            // No AggressiveInlining due to large method size
        //            // Has conventional contract 0->0 (Log(0) is undefined)

        //            // Fill trailing zeros with ones, eg 00010010 becomes 00011111
        //            value |= value >> 01;
        //            value |= value >> 02;
        //            value |= value >> 04;
        //            value |= value >> 08;
        //            value |= value >> 16;

        //            // uint.MaxValue >> 27 is always in range [0 - 31] so we use Unsafe.AddByteOffset to avoid bounds check
        //            return Unsafe.AddByteOffset(
        //                // Using deBruijn sequence, k=2, n=5 (2^5=32) : 0b_0000_0111_1100_0100_1010_1100_1101_1101u
        //                ref MemoryMarshal.GetReference(Log2DeBruijn),
        //                // uint|long -> IntPtr cast on 32-bit platforms does expensive overflow checks not needed here
        //                (IntPtr)(int)((value * 0x07C4ACDDu) >> 27));
        //        }

        //        /// <summary>Returns the integer (ceiling) log of the specified value, base 2.</summary>
        //        /// <param name="value">The value.</param>
        //        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        //        internal static int Log2Ceiling(uint value)
        //        {
        //            int result = Log2(value);
        //            if (PopCount(value) != 1)
        //            {
        //                result++;
        //            }
        //            return result;
        //        }

        //        /// <summary>Returns the integer (ceiling) log of the specified value, base 2.</summary>
        //        /// <param name="value">The value.</param>
        //        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        //        internal static int Log2Ceiling(ulong value)
        //        {
        //            int result = Log2(value);
        //            if (PopCount(value) != 1)
        //            {
        //                result++;
        //            }
        //            return result;
        //        }

        //        /// <summary>
        //        /// Returns the population count (number of bits set) of a mask.
        //        /// Similar in behavior to the x86 instruction POPCNT.
        //        /// </summary>
        //        /// <param name="value">The value.</param>
        //        [Intrinsic]
        //        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        //        [CLSCompliant(false)]
        //        public static int PopCount(uint value)
        //        {
        //            if (Popcnt.IsSupported)
        //            {
        //                return (int)Popcnt.PopCount(value);
        //            }

        //            if (AdvSimd.Arm64.IsSupported)
        //            {
        //                // PopCount works on vector so convert input value to vector first.

        //                Vector64<uint> input = Vector64.CreateScalar(value);
        //                Vector64<byte> aggregated = AdvSimd.Arm64.AddAcross(AdvSimd.PopCount(input.AsByte()));
        //                return aggregated.ToScalar();
        //            }

        //            return SoftwareFallback(value);

        //            static int SoftwareFallback(uint value)
        //            {
        //                const uint c1 = 0x_55555555u;
        //                const uint c2 = 0x_33333333u;
        //                const uint c3 = 0x_0F0F0F0Fu;
        //                const uint c4 = 0x_01010101u;

        //                value -= (value >> 1) & c1;
        //                value = (value & c2) + ((value >> 2) & c2);
        //                value = (((value + (value >> 4)) & c3) * c4) >> 24;

        //                return (int)value;
        //            }
        //        }

        //        /// <summary>
        //        /// Returns the population count (number of bits set) of a mask.
        //        /// Similar in behavior to the x86 instruction POPCNT.
        //        /// </summary>
        //        /// <param name="value">The value.</param>
        //        [Intrinsic]
        //        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        //        [CLSCompliant(false)]
        //        public static int PopCount(ulong value)
        //        {
        //            if (Popcnt.X64.IsSupported)
        //            {
        //                return (int)Popcnt.X64.PopCount(value);
        //            }

        //            if (AdvSimd.Arm64.IsSupported)
        //            {
        //                // PopCount works on vector so convert input value to vector first.
        //                Vector64<ulong> input = Vector64.Create(value);
        //                Vector64<byte> aggregated = AdvSimd.Arm64.AddAcross(AdvSimd.PopCount(input.AsByte()));
        //                return aggregated.ToScalar();
        //            }

        //#if TARGET_32BIT
        //            return PopCount((uint)value) // lo
        //                + PopCount((uint)(value >> 32)); // hi
        //#else
        //            return SoftwareFallback(value);

        //            static int SoftwareFallback(ulong value)
        //            {
        //                const ulong c1 = 0x_55555555_55555555ul;
        //                const ulong c2 = 0x_33333333_33333333ul;
        //                const ulong c3 = 0x_0F0F0F0F_0F0F0F0Ful;
        //                const ulong c4 = 0x_01010101_01010101ul;

        //                value -= (value >> 1) & c1;
        //                value = (value & c2) + ((value >> 2) & c2);
        //                value = (((value + (value >> 4)) & c3) * c4) >> 56;

        //                return (int)value;
        //            }
        //#endif
        //        }

        //        /// <summary>
        //        /// Count the number of trailing zero bits in an integer value.
        //        /// Similar in behavior to the x86 instruction TZCNT.
        //        /// </summary>
        //        /// <param name="value">The value.</param>
        //        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        //        public static int TrailingZeroCount(int value)
        //            => TrailingZeroCount((uint)value);

        //        /// <summary>
        //        /// Count the number of trailing zero bits in an integer value.
        //        /// Similar in behavior to the x86 instruction TZCNT.
        //        /// </summary>
        //        /// <param name="value">The value.</param>
        //        [CLSCompliant(false)]
        //        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        //        public static int TrailingZeroCount(uint value)
        //        {
        //            if (Bmi1.IsSupported)
        //            {
        //                // TZCNT contract is 0->32
        //                return (int)Bmi1.TrailingZeroCount(value);
        //            }

        //            if (ArmBase.IsSupported)
        //            {
        //                return ArmBase.LeadingZeroCount(ArmBase.ReverseElementBits(value));
        //            }

        //            // Unguarded fallback contract is 0->0, BSF contract is 0->undefined
        //            if (value == 0)
        //            {
        //                return 32;
        //            }

        //            if (X86Base.IsSupported)
        //            {
        //                return (int)X86Base.BitScanForward(value);
        //            }

        //            // uint.MaxValue >> 27 is always in range [0 - 31] so we use Unsafe.AddByteOffset to avoid bounds check
        //            return Unsafe.AddByteOffset(
        //                // Using deBruijn sequence, k=2, n=5 (2^5=32) : 0b_0000_0111_0111_1100_1011_0101_0011_0001u
        //                ref MemoryMarshal.GetReference(TrailingZeroCountDeBruijn),
        //                // uint|long -> IntPtr cast on 32-bit platforms does expensive overflow checks not needed here
        //                (IntPtr)(int)(((value & (uint)-(int)value) * 0x077CB531u) >> 27)); // Multi-cast mitigates redundant conv.u8
        //        }

        //        /// <summary>
        //        /// Count the number of trailing zero bits in a mask.
        //        /// Similar in behavior to the x86 instruction TZCNT.
        //        /// </summary>
        //        /// <param name="value">The value.</param>
        //        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        //        public static int TrailingZeroCount(long value)
        //            => TrailingZeroCount((ulong)value);

        //        /// <summary>
        //        /// Count the number of trailing zero bits in a mask.
        //        /// Similar in behavior to the x86 instruction TZCNT.
        //        /// </summary>
        //        /// <param name="value">The value.</param>
        //        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        //        [CLSCompliant(false)]
        //        public static int TrailingZeroCount(ulong value)
        //        {
        //            if (Bmi1.X64.IsSupported)
        //            {
        //                // TZCNT contract is 0->64
        //                return (int)Bmi1.X64.TrailingZeroCount(value);
        //            }

        //            if (ArmBase.Arm64.IsSupported)
        //            {
        //                return ArmBase.Arm64.LeadingZeroCount(ArmBase.Arm64.ReverseElementBits(value));
        //            }

        //            if (X86Base.X64.IsSupported)
        //            {
        //                // BSF contract is 0->undefined
        //                return value == 0 ? 64 : (int)X86Base.X64.BitScanForward(value);
        //            }

        //            uint lo = (uint)value;

        //            if (lo == 0)
        //            {
        //                return 32 + TrailingZeroCount((uint)(value >> 32));
        //            }

        //            return TrailingZeroCount(lo);
        //        }

        /// <summary>
        /// Rotates the specified value left by the specified number of bits.
        /// Similar in behavior to the x86 instruction ROL.
        /// </summary>
        /// <param name="value">The value to rotate.</param>
        /// <param name="offset">The number of bits to rotate by.
        /// Any value outside the range [0..31] is treated as congruent mod 32.</param>
        /// <returns>The rotated value.</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        [CLSCompliant(false)]
        public static uint RotateLeft(uint value, int offset)
            => (value << offset) | (value >> (32 - offset));

        /// <summary>
        /// Rotates the specified value left by the specified number of bits.
        /// Similar in behavior to the x86 instruction ROL.
        /// </summary>
        /// <param name="value">The value to rotate.</param>
        /// <param name="offset">The number of bits to rotate by.
        /// Any value outside the range [0..63] is treated as congruent mod 64.</param>
        /// <returns>The rotated value.</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        [CLSCompliant(false)]
        public static ulong RotateLeft(ulong value, int offset)
            => (value << offset) | (value >> (64 - offset));

        /// <summary>
        /// Rotates the specified value right by the specified number of bits.
        /// Similar in behavior to the x86 instruction ROR.
        /// </summary>
        /// <param name="value">The value to rotate.</param>
        /// <param name="offset">The number of bits to rotate by.
        /// Any value outside the range [0..31] is treated as congruent mod 32.</param>
        /// <returns>The rotated value.</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        [CLSCompliant(false)]
        public static uint RotateRight(uint value, int offset)
            => (value >> offset) | (value << (32 - offset));

        /// <summary>
        /// Rotates the specified value right by the specified number of bits.
        /// Similar in behavior to the x86 instruction ROR.
        /// </summary>
        /// <param name="value">The value to rotate.</param>
        /// <param name="offset">The number of bits to rotate by.
        /// Any value outside the range [0..63] is treated as congruent mod 64.</param>
        /// <returns>The rotated value.</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        [CLSCompliant(false)]
        public static ulong RotateRight(ulong value, int offset)
            => (value >> offset) | (value << (64 - offset));
    }
}

#endif